Rhesus rhadinovirus is a gamma-2 herpesvirus that is closely related to human herpesvirus 8 (HHV- 8)/Kaposi's sarcoma-associated herpesvirus (KSHV). In simian immunodeficiency virus (SIV) infected rhesus macaques (RM), RRV is associated with B cell hyperplasia and persistent lymphadenopathy that closely resemble multicentric Castleman's disease (MCD). More recently, RRV is found to be associated with non- Hodgkin's lymphoma (NHL), another disease manifestation that HHV-8 is found to be associated in a percentage of HIV-1 infected individuals. The close genetic similarity between RRV and HHV8 and the similar disease manifestations observed in animals/individuals infected with these viruses in conditions of immune deficiency, suggests that RRV infection of RM is an excellent animal model to identify HHV8 determinants of pathogenesis. Thus, the long-term goal of this application and the underlying hypothesis driving these studies are that RRV is directly associated with the B cell disease manifestations mentioned above in SIV-infected RM. To address this goal the following Specific Aims are proposed: Specific Aim 1: Identify differences between pathogenic and non-pathogenic isolates of RRV. Specific Aim 2: Construct a pathogenic bacterial artifical chromosome (BAG) of RRV strain 17577 from c3 to facilitate the generation of mutants in RRV. Specific Aim 3: To develop transposon mutagenesis for the RRV BAG to identify viral ORFs associated with RRV-associated disease-like patterns in vitro. Specific Aim 4: In vivo pathogenesis of mutant RRVs with targeted mutations defined ORFs identified in SA3 associated with distinct in vitro properties. The results form these proposed studies should provide new insight into how RRV induces RRV-associated disease, and serve as a means to elucidate the role of HHV8 in HHV8-associated disease.